Patch "drm/nouveau: Fix deadlock on runtime suspend" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

drm/nouveau: Fix deadlock on runtime suspend

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-nouveau-fix-deadlock-on-runtime-suspend.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lukas Wunner <[email protected]>
Date: Sun, 11 Feb 2018 10:38:28 +0100
Subject: drm/nouveau: Fix deadlock on runtime suspend

From: Lukas Wunner <[email protected]>

commit d61a5c1063515e855bedb1b81e20e50b0ac3541e upstream.

nouveau's ->runtime_suspend hook calls drm_kms_helper_poll_disable(), which waits for the output poll worker to finish if it's running.

The output poll worker meanwhile calls pm_runtime_get_sync() in nouveau_connector_detect() which waits for the ongoing suspend to finish, causing a deadlock.

Fix by not acquiring a runtime PM ref if nouveau_connector_detect() is called in the output poll worker's context. This is safe because the poll worker is only enabled while runtime active and we know that ->runtime_suspend waits for it to finish.

Other contexts calling nouveau_connector_detect() do require a runtime PM ref, these comprise:

status_store() drm sysfs interface
->fill_modes drm callback
drm_fb_helper_probe_connector_modes()
drm_mode_getconnector()
nouveau_connector_hotplug()
nouveau_display_hpd_work()
nv17_tv_set_property()

Stack trace for posterity:

  INFO: task kworker/0:1:58 blocked for more than 120 seconds.
  Workqueue: events output_poll_execute [drm_kms_helper]
  Call Trace:
   schedule+0x28/0x80
   rpm_resume+0x107/0x6e0
   __pm_runtime_resume+0x47/0x70
   nouveau_connector_detect+0x7e/0x4a0 [nouveau]
   nouveau_connector_detect_lvds+0x132/0x180 [nouveau]
   drm_helper_probe_detect_ctx+0x85/0xd0 [drm_kms_helper]
   output_poll_execute+0x11e/0x1c0 [drm_kms_helper]
   process_one_work+0x184/0x380
   worker_thread+0x2e/0x390

  INFO: task kworker/0:2:252 blocked for more than 120 seconds.
  Workqueue: pm pm_runtime_work
  Call Trace:
   schedule+0x28/0x80
   schedule_timeout+0x1e3/0x370
   wait_for_completion+0x123/0x190
   flush_work+0x142/0x1c0
   nouveau_pmops_runtime_suspend+0x7e/0xd0 [nouveau]
   pci_pm_runtime_suspend+0x5c/0x180
   vga_switcheroo_runtime_suspend+0x1e/0xa0
   __rpm_callback+0xc1/0x200
   rpm_callback+0x1f/0x70
   rpm_suspend+0x13c/0x640
   pm_runtime_work+0x6e/0x90
   process_one_work+0x184/0x380
   worker_thread+0x2e/0x390

Bugzilla: https://bugs.archlinux.org/task/53497
Bugzilla: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=870523
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70388#c33

---
 drivers/gpu/drm/nouveau/nouveau_connector.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

@@ -253,9 +253,15 @@ nouveau_connector_detect(struct drm_conn
 		nv_connector->edid = NULL;
 	}
 
-	ret = pm_runtime_get_sync(connector->dev->dev);
-	if (ret < 0 && ret != -EACCES)
-		return conn_status;
+	/* Outputs are only polled while runtime active, so acquiring a
+	 * runtime PM ref here is unnecessary (and would deadlock upon
+	 * runtime suspend because it waits for polling to finish).
+	 */
+	if (!drm_kms_helper_is_poll_worker()) {
+		ret = pm_runtime_get_sync(connector->dev->dev);
+		if (ret < 0 && ret != -EACCES)
+			return conn_status;
+	}
 
 	nv_encoder = nouveau_connector_ddc_detect(connector);
 	if (nv_encoder && (i2c = nv_encoder->i2c) != NULL) {

@@ -323,8 +329,10 @@ detect_analog:
 
  out:
 
-	pm_runtime_mark_last_busy(connector->dev->dev);
-	pm_runtime_put_autosuspend(connector->dev->dev);
+	if (!drm_kms_helper_is_poll_worker()) {
+		pm_runtime_mark_last_busy(connector->dev->dev);
+		pm_runtime_put_autosuspend(connector->dev->dev);
+	}
 
 	return conn_status;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/workqueue-allow-retrieval-of-current-task-s-work-struct.patch queue-4.4/drm-radeon-fix-deadlock-on-runtime-suspend.patch queue-4.4/drm-amdgpu-fix-deadlock-on-runtime-suspend.patch queue-4.4/drm-allow-determining-if-current-task-is-output-poll-worker.patch queue-4.4/drm-nouveau-fix-deadlock-on-runtime-suspend.patch